White matter anatomy
The CNS is comprised of white and grey matter. The white matter is essentially cabling linking one part to another. In places these cables are aggregated to form distinct bundles.
There are three types of white matter cables as shown in the following table:
You need to know some of the names for the different tracts, particularly what type of tract they are. The following tables gives the more common ones you need to know:
There are three types of white matter cables as shown in the following table:
| Tract | Connections |
|---|---|
| Projection tracts | Connect higher centers of the brain (those beyond the brain stem) with lower centers (e.g. brainstem and spinal cord) |
| Commissural tracts | Connect the two hemispheres together |
| Association tracts | Connect regions of the same hemisphere. Long association connect separate lodes together whereas short association fibers connect separate gyri of the same lobe |
You need to know some of the names for the different tracts, particularly what type of tract they are. The following tables gives the more common ones you need to know:
| Tract type | Examples | Description |
|---|---|---|
| Projection | Corticospinal | Efferent projection fibers that connect motor cortex to the brain stem and spinal cord |
| Corticobulbar | Efferent projection fibers that connect motor cortex to the brain stem and spinal cord | |
| Corona Radiata | Fibers to and from virtually all cortical areas fan out superolaterally from the internal capsule | |
| Internal Capsule | Major conduit of fibers to and from the cerebral cortex | |
| Geniculocalcarine Tract (optic radiation) | Connects the lateral geniculate nucleus to occipital (primary visual) cortex | |
| Commissural | Corpus Callosum | The largest white matter fiber bundle, the corpus callosum is a massive accumulation of fibers connecting corresponding areas of cortex between the hemispheres |
| Anterior Commissure | The anterior commissure crosses through the lamina terminalis. Its anterior fibers connect the olfactory bulbs and nuclei; its posterior fibers connect middle and inferior temporal gyri | |
| Association | Cingulum | Interconnects portions of the frontal, parietal, and temporal lobes |
| Superior Occipitofrontal Fasciculus | Connects occipital and frontal lobes | |
| Inferior Occipitofrontal Fasciculus | Connects the occipital and frontal lobes | |
| Uncinate Fasciculus | Connects the orbital and inferior frontal gyri of the frontal lobe to the anterior temporal lobe | |
| Superior Longitudinal (arcuate) Fasciculus | Connects the frontal lobe cortex to parietal, temporal, and occipital lobe cortices (the largest association bundle) | |
| Inferior Longitudinal (occipitotemporal) Fasciculus | Connects temporal and occipital lobe cortices |
